A battery management system can be used to monitor a battery pack that includes one or more battery cells, and to collect and analyze monitoring data indicative of the status of the battery pack in order to keep the battery pack working in a normal condition. The monitoring data typically includes voltages and currents of the battery cells. Generally, the battery pack voltage can be obtained by adding the voltages of the battery cells, which are sampled at the same time. However, it can be difficult and/or costly to use a global clock to sample the voltages and the currents of the battery cells synchronously since the battery cells are isolated from each other. Without a global clock, monitoring data may be sampled cycle-by-cycle independently by configuring a local clock to each battery cell. However, even if all the local clocks are designed to be the same as each other, small errors induced by variations in the environment can accumulate, affecting the monitoring data and hence the performance of the battery management system.
FIG. 1 illustrates an asynchronous data sampling diagram 100 for a conventional battery management system. In the example of FIG. 1, a data sampling diagram 102 for a first battery BATT1 and a data sampling diagram 104 for a second battery BATT2 are shown. The BATT1 and the BATT2 can be any two of the battery cells in the battery pack. The battery management system can sample the monitoring data indicative of the status of a corresponding battery cell periodically. The sample periods for the BATT1 and the BATT2 are designed to be the same value TN. However, sample periods for the BATT1 are asynchronous with sample periods for the BATT2 since the battery management system samples each battery cell according to its own sampling timing.
If the battery management system intends to get sample data for the battery pack at time TS, the battery management system will get the latest sample data D1(N) for the BATT1 obtained at the end of sample period T1(N), and will also get the latest sample data D2(N−1) for the BATT2 obtained at the end of sample period T2(N−1). As such, a time difference between the end of the sample period T1(N) and the end of the sample period T2(N−1) may be almost one sample period TN. Since the sample period TN can be several milliseconds or even longer, the time difference between the end of the sample period T1(N) and the end of the sample period T2(N−1) may be several milliseconds.
In some applications, such as electric vehicle/hybrid electric vehicle applications, a load current can fluctuate frequently. As such, the load current at the end of the sample period T1(N) and the load current at the end of the sample period T2(N−1) may not be the same value since the time difference between the end of the sample period T1(N) and the end of the sample period T2(N−1) may be several milliseconds. Hence, the sample data D1(N) for the BATT1 obtained at the end of sample period T1(N) and the sample data D2(N) for the BATT2 obtained at the end of sample period T2(N−1) may be sampled in different environments, which may decrease the accuracy of the battery management system.